Many of today's vehicles incorporate a hybrid drive technology that incorporates at least partial use of an electrical motor to provide the driving force for the vehicle. Electric motors do not produce the well-known sounds of an internal combustion engine that pedestrians and bystanders normally associate with the presence of a vehicle. A hybrid drive typically comprises an electric motor and an engine working together to provide drive for the vehicle and charge batteries in the vehicle. When an engine is operating in a hybrid vehicle, the engine speed may not represent the speed of the vehicle. Further, when a hybrid vehicle is driven by the electric motor, the operation of the motor does not provide sufficient sound to give notice to pedestrians and bystanders of the presence, motion, and/or operating characteristics of the vehicle.
By contrast, the sounds generated by an internal combustion engine are well known. The sound of an accelerating vehicle, the sound of a large diesel truck, or the sound of a V8 engine compared to a smaller four cylinder engine are indicators to pedestrians and bystanders of the size, nature, and operating status of a vehicle.
In addition to the familiarity of the sounds of vehicles, the public is also aware of the use of sound as a branding tool to identify the manufacturer of a product, as typified by many television commercials. Modern vehicles typically comprise a high-powered sound system for use by the occupants of a vehicle. However, sound systems are not used to provide branding information and vehicle operating status information to pedestrians and bystanders within audible range of a vehicle.